Surface-Oxidized Iron–Cobalt–Nickel Alloy with Continuous Variable Composition for Hydrogen and Oxygen Evolution Reaction

Abstract

Composition is the key to optimizing the electroactivity of the alloy-based electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a library of surface-oxidized iron–cobalt–nickel-based (FeCoNi-based) alloys, FeCoNi and FeCoNi/OH, with continuous variable compositions are built as HER and OER electrocatalysts. The FeCoNi alloys with a low content of Fe display higher HER intrinsic activity, while the alloys with low Co content exhibit higher OER activity. Because the electrochemical specific area is evidently increasing with the addition of Fe and Co, the Fe6Co4Ni0 exhibits the outstanding HER activity and stability. Benefiting from the synergistic effect, the alloys’ HER activity for most compositions is enhanced by the surface hydroxides. However, the surface-oxidized hydroxides barely affect OER activity for most compositions of the alloys. After a year of storage, the FeCoNi and FeCoNi/OH electrodes exhibit high stability for HER but not for OER. These trends may help to exploit higher activity electrocatalysts for hydrogen production by water electrolysis.

Convenient Synthesis of NiCo Alloy Nanoparticles Encapsulated by N-Doped Porous Carbon for the Oxygen Evolution Reaction

“…The high-resolution N 1s spectrum (Figure c) comprises four peaks, which are located at 397.2, 398.7, 400.3, and 403 eV, corresponding to pyridine N, pyrrole N, graphite N, and oxidized N, respectively. − Pyridine N is favorable for anchoring and dispersion of the alloy . Moreover, pyridine N and graphite N can effectively improve the conductivity of materials. , As shown in Figure d, there are two peaks located at 853.1 and 856 eV in the Ni 2p spectrum corresponding to the Ni 2p 3/2 orbits of the Ni metallic state and the Ni 2+ oxidation state, respectively. , Peaks of 870.2 and 873.6 eV correspond to the Ni 2p 1/2 orbits of the metallic state and Ni 2+ , respectively, while the two peaks at 860.9 and 879.1 eV are satellite peaks. − The deconvolution of the Co 2p spectrum results in six peaks. The peaks at 778.6 and 796.5 eV belong to the 2p 3/2 and 2p 1/2 orbits of Co 0 , respectively, and the peaks at 781.2 and 796.5 eV belong to the 2p 3/2 and 2p 1/2 orbits of Co 2+ , respectively. − Furthermore, two satellite peaks were observed at 786.5 and 803.5 eV, as shown in Figure e.…”

“…33,34 As shown in Figure 3d, there are two peaks located at 853.1 and 856 eV in the Ni 2p spectrum corresponding to the Ni 2p 3/2 orbits of the Ni metallic state and the Ni 2+ oxidation state, respectively. 35,36 Peaks of 870.2 and 873.6 eV correspond to the Ni 2p 1/2 orbits of the metallic state and Ni 2+ , respectively, while the two peaks at 860.9 and 879.1 eV are satellite peaks. 37−39 The deconvolution of the Co 2p spectrum results in six peaks.…”

A crystalline/amorphous FeCo alloy/FeCoNi-Pi bifunctional electrocatalyst for efficient overall water splitting

“…In general, the HER involves the adsorption and desorption of protons and can be classified into two mechanisms: the Volmer-Heyrovsky process and the Volmer-Tafel process. 47,48 It is crucial to mention that FC has a Tafel slope of 117.7 mV dec −1 , meaning that the rate-limiting step of FC for HER is the Volmer step. 36 This result indicates that the HER performance of the FeCo alloy is limited by the poor water dissociation ability.…”